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141.
Joy Sanyal Priyanka Dasgupta Shinjiro Kanae 《Singapore journal of tropical geography》2020,41(2):284-298
Dam-related downstream adjustments of riverbeds are normally investigated by analysing the trend in sediment supply and high flow events during the pre- and post-dam periods. The required data for existing predictive models is not measured at river gauges, which limits the application of these tools. We derived the frequency of sediment-transporting streamflow events (T*) and upstream sediment supply (S*) in the pre- and post-dam periods with widely available gauged records and predicted changes in the downstream riverbed by adapting an existing model. Ten gauging stations in the Godavari River Basin, India, located downstream of dams, were chosen as study sites. Annually surveyed cross-sections at each site validated the accuracy of the predicted dam-related downstream changes. Then, a regression equation (R2 = 0.75) was established between T*/S* (independent variable) and changes in the downstream bed elevation (dependent variable) for the Godavari Basin. We recommended that similar local empirical equations be formulated for larger river basins. Models of large-scale rainfall-runoff and sediment transport processes that can account for the influence of dams, such as the Soil & Water Assessment Tool, can be paired with the proposed regression equation to estimate dam-related downstream erosion and deposition with globally available data. 相似文献
142.
S. S. De B. K. Sarkar B. Ghosh A. C. Sen S. Bandyopadhyay S. K. Adhikari 《Earth, Moon, and Planets》1991,53(1):1-10
Enhancement of conductivity tensor modification within the ionospheric plasma by electron density modulation through the temperature dependence of the recombination rates of different ionspecies caused due to electron temperature modulation during high-power wave propagation is studied. Variation of Hall and Pedersen conductivities of the ionosphere has been investigated in the height range between 85 km to 250 km. The generation of waves at the modulation frequency and its harmonics in the ELF, VLF bands in the process is discussed. 相似文献
143.
Mausumi Dikpati Peter A. Gilman Giuliana de Toma Siddhartha S. Ghosh 《Solar physics》2007,245(1):1-17
We use the flux-transport dynamo prediction scheme introduced by Dikpati, de Toma, and Gilman (Geophys. Res. Lett.
33, L05102, 2006) to make separate simulations and predictions of sunspot cycle peaks for northern and southern hemispheres. Despite the division
of the data, the skill level achieved is only slightly lower than that achieved for the sum of both hemispheres. The model
shows skill at simulating and predicting the difference in peaks between North and South, provided that difference is more
than a few percent. The simulation and prediction skill is achieved without adjustment to any parameters of the model that
were used when peaks for the sum of North and South sunspot areas was simulated. The results are also very insensitive to
the averaging length applied to the input data, provided the simulations and predictions are for peaks defined by averaging
the observations over at least 13 rotations. However, in its present form, the model is not capable of skillfully simulating
or predicting short-time-scale features of individual solar cycles. 相似文献
144.
H. N. Bhattacharya Indranil Chakraborty Kaushik K. Ghosh 《Journal of Earth System Science》2007,116(3):245-259
Banded iron-formations (BIF) form an important part of the Archean supracrustal belts of the Jharkhand-Orissa region, India.
Major, trace and REE chemistry of the banded iron-formation of the Gandhamardan, Deo Nala, Gorumahisani and Noamundi sections
of the Jharkhand-Orissa region are utilized to explore the source of metals and to address the thermal regime of the basin
floor and the redox conditions of the archean sea. Hydrothermal fluids of variable temperatures might have contributed the
major part of the Fe and other trace elements to the studied banded iron-formations. Diagenetic fluids from the sea floor
sediments and river water might have played a subdued role in supplying the Fe and other elements for the banded iron-formations. 相似文献
145.
Pranab Ghosh 《Journal of Astrophysics and Astronomy》2002,23(1-2):107-113
I summarize X-ray diagnostic studies of cosmic star formation history in terms of evolutionary schemes for X-ray binary evolution
in normal galaxies with evolving star formation. Deep X-ray imaging studies byChandra andXMM-Newton are now beginning to constrain both the X-ray luminosity evolution of galaxies and the logN- logS diagnostics of the X-ray background. I discuss these in the above context, summarizing current understanding and future prospects. 相似文献
146.
Prosenjit Ghosh Jess Adkins Brian Balta Edwin A. Schauble John M. Eiler 《Geochimica et cosmochimica acta》2006,70(6):1439-1456
The abundance of the doubly substituted CO2 isotopologue, 13C18O16O, in CO2 produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of 13C-18O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 °C by the function: Δ47 = 0.0592 · 106 · T−2 − 0.02, where Δ47 is the enrichment, in per mil, of 13C18O16O in CO2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO2 isotopologues, and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry, where the temperature-dependent property of interest is the state of ordering of 13C and 18O in the carbonate lattice (i.e., bound together vs. separated into different CO32− units), and not the bulk δ18O or δ13C values. Current analytical methods limit precision of this thermometer to ca. ± 2 °C, 1σ. A key feature of this thermometer is that it is thermodynamically based, like the traditional carbonate-water paleothermometer, and so is suitable for interpolation and even modest extrapolation, yet is rigorously independent of the δ18O of water and δ13C of DIC from which carbonate grew. Thus, this technique can be applied to parts of the geological record where the stable isotope compositions of waters are unknown. Moreover, simultaneous determinations of Δ47 and δ18O for carbonates will constrain the δ18O of water from which they grew. 相似文献
147.
S. Adhikari Ph.D. L. Ghosh Ph.D. S. Ayyappan Ph.D. 《International Journal of Environmental Science and Technology》2006,3(3):289-296
Influence of pH (5.5, 7.0 and 8.5) and alkalinity (40 to 200 mg/L as CaCO3) on the accumulation of Pb (NO3)2 CdCl2, H2O and K2Cr2O7 to Labeo rohita (Hamilton) was investigated in the laboratory. Highest accumulation of Pb and Cr in whole fish occurred at pH 5.5 and at alkalinity level of 40 to 46 mg/L as CaCO3 compared to 7.0 and 8.5. In case of Cd maximum accumulation occurred at pH 7.0 and at alkalinity of 100 mg/L as CaCO3 than that of pH 5.5 and 8.5 and alkalinity 42 and 156 mg/L as CaCO3. Maximum accumulation of lead and chromium occurred at total alkalinity level of 40 and 46 mg/L as CaCO3, respectively while maximum accumulation of cadmium occurred at an alkalinity level of 200 mg/L as CaCO3. A significant (p<0.05) linear relationship was demonstrated between increasing pH/ alkalinity and decreasing accumulation in Pb and Cr treatment at all exposure period while for Cd there was no significant linear relationship established. 相似文献
148.
R.R. Daniel S.K. Ghosh K.V.K. Iyengar T.N. Rengarajan S.N. Tandon R.P. Verma 《Icarus》1982,49(2):205-212
We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find TD, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of TD and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm. 相似文献
149.
Nine different types of cross‐stratified packages from the coal‐bearing, deltaic succession of the Barakar Formation (Permian) of the Satpura Gondwana Basin, central India, are described. The deposits are characterized by periodic mudstone drapes, reactivation surfaces including all other features suggestive of deposition from periodically unsteady, tidally‐influenced flows. The inferred flow patterns varied from purely bidirectional to pulsating unidirectional. The different types of cross‐stratified packages are interpreted to have resulted from superimposition of ebb‐oriented, steady, unidirectional fluvial currents of variable strength on the tidal flow in a deltaic setting. The study helps to distinguish cross‐strata that may develop in settings where fluvial and tidal currents interact. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
150.
Floods are the most frequently occurring natural hazard in Canada. An in-depth understanding of flood seasonality and its drivers at a national scale is essential. Here, a circular, statistics-based approach is implemented to understand the seasonality of annual-maximum floods (streamflow) and to identify their responsible drivers across Canada. Nearly 80% and 70% of flood events were found to occur during spring and summer in eastern and western watersheds across Canada, respectively. Flooding in the eastern and western watersheds was primarily driven by snowmelt and extreme precipitation, respectively. This observation suggests that increases in temperature have led to early spring snowmelt-induced floods throughout eastern Canada. Our results indicate that precipitation (snowmelt) variability can exert large controls on the magnitude of flood peaks in western (eastern) watersheds in Canada. Further, the nonstationarity of flood peaks is modelled to account for impact of the dynamic behaviour of the identified flood drivers on extreme-flood magnitude by using a cluster of 74 generalized additive models for location scale and shape models, which can capture both the linear and nonlinear characteristics of flood-peak changes and can model its dependence on external covariates. Using nonstationary frequency analysis, we find that increasing precipitation and snowmelt magnitudes directly resulted in a significant increase in 50-year streamflow. Our results highlight an east–west asymmetry in flood seasonality, indicating the existence of a climate signal in flood observations. The understating of flood seasonality and flood responses under the dynamic characteristics of precipitation and snowmelt extremes may facilitate the predictability of such events, which can aid in predicting and managing their impacts. 相似文献